In manufacture of a semiconductor wafer, it is important for securing a profit to start a manufacture process rapidly and make a shift to mass production system of high yield early.
In order to achieve this object, various inspection/measurement devices are introduced into manufacture lines. In the process start stage, it is conducted to, for example, change process conditions intentionally, making a plurality of wafers or chips, inspecting the wafers or chips, and determining process conditions on the basis of a result of the inspection, with the object of determining process conditions capable of forming a desired circuit pattern early.
On the other hand, wafer inspection in a mass production stage is conducted for monitoring. In other words, in an intermediate stage of wafer manufacture, a wafer is sampled and inspected, and it is checked whether a defect occurs on a surface of the wafer or whether there is an abnormality in a circuit pattern formed on the wafer surface. In a case where a defect or an abnormality in the circuit pattern is detected because of inspection, a cause thereof is investigated and a necessary countermeasure is taken.
As a representative inspection device used in such a process start stage or a mass production stage, there is an optical wafer inspection device. For example, JR-A-2000-105203 (Patent Literature 1) discloses a technique of picking up an optical image of a wafer surface by means of bright visual field illumination and inspecting a defect by comparing the optical image of the wafer surface with an image of a good article region (for example, an image of an adjacent chip). However, such an optical inspection device undergoes influence of an illumination wavelength thereof, and a resolution limit of an acquired image becomes approximately several hundred nanometers. As regards a defect of several ten nanometers order on the wafer, therefore, the optical inspection device can detect only whether there is a defect. When conducting a detailed defect analysis, a different defect observation device having a higher imaging resolution is needed.
The defect observation device is a device that picks up an image in a defect position on a wafer by using an output of the inspection device and outputs the image. In the semiconductor manufacture process, size shrinking is promoted. As a result, a defect size reaches an order of several nm. In order to observe a defect in detail, therefore, a resolution of several nm order is needed. Accordingly, an observation device (hereafter referred to as review SEM) using a scanning electron microscope (SEM) has been widely used in recent years. In a mass production line of semiconductor, automation of the observation work is desired. The review SEM mounts a function of ADR (Automatic Defect Review) for automatically collecting images in defect positions in a sample and ADC (Automatic Defect Classification) for automatically classifying approximately several hundred defect images acquired by the ADR according to occurrence causes or features of exterior view. By the way, a defect position coordinate (coordinate information indicating a position of a defect on the sample) output by the inspection device includes an error. Therefore, the ADR has a function of re-detecting a defect from an SEM image picked up with a wide visual field around a defect position coordinate output by the inspection device and picking up an image in the re-detected defect position with high magnification. As a method for detecting defects from the SEM image, JP-A-2001-189358 (Patent Literature 2) states a method of using an image obtained by picking up an image of an area where the same circuit pattern as that of a defect region is formed, as a reference image and detecting a defect by comparing an image obtained by picking up an image of defect region with the reference image. Furthermore, JP-A-2007-40910 (Patent Literature 3) states a method of detecting a defect from one image obtained by picking up an image of a defect region. As one method of automatic classification, JP-A-21803 (Patent Literature 4) states a method of quantizing an exterior view feature quantity of a defect region by conducting image processing and classifying defects by using a neural network. Furthermore, as a method capable of easily coping with even in a case where the number of kinds of defects to be classified is many, JP-A 2007-225531 (Patent Literature 5) states a method of classifying defects by combining a rule base classification method with a teaching classification method.